The invention relates to a technique for controlling switching of a traveling mode of a hybrid electric vehicle.
Of recently-developed hybrid electric vehicles, some vehicles are known as being able to switch among an EV mode in which the vehicle travels by means of drive motors (electric motors) and by use of electric power fed from a drive battery without activating an engine, a series mode in which the vehicle travels by means of the electric motors while generating electric power by causing the engine to actuate a generator, and a parallel mode in which the vehicle travels by means of both the engine and the electric motors.
In a hybrid electric vehicle capable of traveling in a parallel mode, driving force can be transmitted from the engine to drive shafts by way of a transmission and a clutch. In the parallel mode, the clutch is connected, and gear-shifting of the transmission is controlled to transmit the driving force to drive wheels.
Patent Document 1 discloses a hybrid electric vehicle capable of automatically switching among the EV mode, the series mode, and the parallel mode in accordance with a state of charge of a drive battery and a traveling velocity.
Patent Document 1 also discloses a technique of implementing switching of the mode to the parallel mode when the state of charge of the battery has anomalously fallen for reasons of a failure of the generator, or the like, to thus enable the vehicle to travel in emergency.
[Patent Document 1] International Publication No. WO-2011-129196